Self-Location Estimation Method and Self-Location Estimation Device

ABSTRACT

A self-location estimation method includes detecting a traffic sign in a vicinity of a vehicle; determining a current location of the vehicle; acquiring height information of the detected traffic sign from map data in which two-dimensional coordinate information and height information of a traffic sign existing in a vicinity of a road are recorded, based on a relative location of the detected traffic sign with respect to the vehicle and the current location; and estimating a height at which the vehicle is present according to the height information acquired from the map data.

TECHNICAL FIELD

The present invention relates to a self-location estimation method and aself-location estimation device.

BACKGROUND

In JP 2006-317286 A, a technology for determining whether the currentlocation of a vehicle is on an ordinary road or an expressway, based onwhether, in an image of the vicinity of the vehicle captured by acamera, an ordinary road identifying image for identifying that thevehicle is traveling on an ordinary road or an expressway identifyingimage for identifying that the vehicle is traveling on an expressway isincluded is described.

SUMMARY

Although the technology described in JP 2006-317286 A is capable ofdiscriminating between roads the road types of which are different fromeach other, the technology is incapable of discriminating betweendifferent roads the road types of which are the same.

Thus, when different roads the road types of which are the samerespectively exist at different heights and the two-dimensionallocations of the roads are close to each other, it sometimes becomesimpossible to determine on which one of the roads the vehicle ispresent.

An object of the present invention is to enable determination of onwhich one of roads existing at different heights a vehicle is present.

According to one aspect of the present invention, there is provided aself-location estimation method including: detecting a traffic sign in avicinity of a vehicle; determining a current location of the vehicle;acquiring height information of the detected traffic sign from map datain which two-dimensional coordinate information and height informationof a traffic sign existing in a vicinity of a road are recorded, basedon a relative location of the detected traffic sign with respect to thevehicle and the current location; and estimating a height at which thevehicle is present according to the height information acquired from themap data.

According to the aspect of the present invention, it is possible todetermine on which one of roads existing at different heights a vehicleis present.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an example of a drivingassistance device of an embodiment;

FIG. 2 is an explanatory diagram of an example of a self-locationestimation method of the embodiment;

FIG. 3 is a block diagram illustrative of an example of a functionalconfiguration of an electronic control unit (ECU) illustrated in FIG. 1;

FIG. 4 is an explanatory diagram of an example of a calculation methodof two-dimensional coordinates of a traffic sign;

FIG. 5 is a flowchart of an example of a driving assistance method ofthe embodiment;

and

FIG. 6 is a flowchart of an example of a self-location estimation methodillustrated in FIG. 5.

DETAILED DESCRIPTION

An embodiment of the present invention will now be described withreference to the drawings.

(Configuration)

FIG. 1 is now referred to. A driving assistance device 1 performsautomatic-driving control for making a vehicle (hereinafter, referred toas “vehicle”) on which the driving assistance device 1 is mountedautomatic-drive without involvement of a driver and driving assistancecontrol for assisting a driver in driving the vehicle, based on a travelenvironment in the surroundings of the vehicle.

The driving assistance control may include not only travel control, suchas automatic-steering, automatic-braking, constant speed travelingcontrol, and lane keeping control, but also outputting a messageprompting the driver to perform a steering operation or a decelerationoperation.

The driving assistance device 1 includes external sensors 3, internalsensors 4, a positioning device 5, a map database 6, a navigation system7, an electronic control unit (ECU) 8, a human machine interface (HMI)9, and actuators 10. Note that a map database is denoted as “map DB” inattached drawings.

The external sensors 3 are sensors that detect a surrounding environmentaround the vehicle, such as an object in the surroundings of thevehicle. The external sensors 3 may include a camera 11 and a rangingdevice 12. The camera 11 and the ranging device 12 detect a surroundingenvironment around the vehicle, such as objects existing in thesurroundings of the vehicle (for example, another vehicle, a pedestrian,white lines such as a lane boundary line and a lane marking, and groundobjects that are installed on a road or in the vicinity of the road,such as a traffic light, a stop line, a traffic sign, a building, autility pole, a curb, and a crosswalk), relative locations of suchobjects with respect to the vehicle, relative distances between thevehicle and the objects, and the like.

The camera 11 may be, for example, a stereo camera. The camera 11 may becomposed of monocular cameras, and, by capturing images of an identicalobject from a plurality of perspectives using the monocular cameras, adistance to the object may be calculated. The distance to the object maybe calculated based on a ground contact position of the object detectedfrom captured images captured by the monocular cameras.

The ranging device 12 may be, for example, a laser range-finder (LRF) ora radar.

The camera 11 and the ranging device 12 output surrounding environmentinformation, which is information on the detected surroundingenvironment, to the ECU 8 and the navigation system 7.

The internal sensors 4 are sensors that detect a travel state of thevehicle. The internal sensors 4 may include, for example, a wheel speedsensor 13 and a gyro-sensor 14.

The wheel speed sensor 13 detects a wheel speed of the vehicle. Thegyro-sensor 14 detects a pitch angular velocity, a roll angularvelocity, and a yaw angular velocity of the vehicle. The wheel speedsensor 13 and the gyro-sensor 14 output travel state information, whichis information on the detected travel state, to the ECU 8 and thenavigation system 7.

The positioning device 5 receives radio waves from a plurality ofnavigation satellites and thereby acquires a current location of thevehicle and outputs the acquired current location of the vehicle to theECU 8 and the navigation system 7. The positioning device 5 may have,for example, a global positioning system (GPS) receiver or anotherglobal navigation satellite system (GNSS) receiver other than a GPSreceiver.

The map database 6 stores road map data. The road map data includeshapes (lane shapes) and two-dimensional coordinates (for example,latitude and longitude) of white lines, such as lane boundary lines andlane markings, heights of roads and white lines, two-dimensionalcoordinate information (for example, latitude and longitude) and heightinformation of ground objects that are installed on roads and in thevicinities of the roads, such as traffic lights, stop lines, trafficsigns, buildings, utility poles, curbs, and crosswalks.

The road map data may also include information on road types, gradientsof roads, the numbers of lanes, legal velocities (velocity limits), roadwidths, presence or absence of junctions, and the like. In the roadtypes, for example, an ordinary road and an expressway may be included.

The map database 6 is referred to by the ECU 8 and the navigation system7.

The navigation system 7 performs route guidance to a destination that isset on a map by the driver of the vehicle for a passenger on thevehicle. The navigation system 7 estimates a current location of thevehicle, using various types of information input from the externalsensors 3, the internal sensors 4, and the positioning device 5,generates a route to the destination, and performs route guidance for apassenger. The navigation system 7 outputs the route information to theECU 8.

The ECU 8 estimates a current location of the vehicle and sets a targettravel trajectory on which the vehicle is required to travel, based onthe estimated current location, the road map data in the map database 6,the route information output from the navigation system 7, thesurrounding environment, and the travel state of the vehicle. The ECU 8performs automatic-driving control and driving assistance control of thevehicle, based on the set target travel trajectory, and drives theactuators 10 and thereby controls travel of the vehicle.

The external sensors 3, the internal sensors 4, the positioning device5, the map database 6, and the ECU 8 constitute a self-locationestimation device 2 according to the embodiment.

The ECU 8 includes a processor 15 and peripheral components, such as astorage device 16. The processor 15 may be, for example, a centralprocessing unit (CPU) or a micro-processing unit (MPU).

The storage device 16 may include a semiconductor storage device, amagnetic storage device, and an optical storage device. The storagedevice 16 may include registers, a cache memory, and a memory, such as aread only memory (ROM) and a random access memory (RAM), that are usedas a main storage device.

Note that the ECU 8 may be achieved by a functional logic circuit thatis implemented in a general-purpose semiconductor integrated circuit.For example, the ECU 8 may include a programmable logic device (PLD),such as a field-programmable gate array (FPGA), and the like.

The HMI 9 is an interface for inputting and outputting informationbetween a passenger on the vehicle and the navigation system 7 and ECU8.

The HMI 9 may accept, for example, an input operation of inputting adestination to the navigation system 7 that is performed by thepassenger. The HMI 9 may, for example, output driving guidance given bythe navigation system 7 or road guidance information based on the roadmap data of the surroundings of the vehicle.

The actuators 10 operate the steering wheel, accelerator opening, and abraking device of the vehicle according to a control signal output fromthe ECU 8 and thereby generate vehicle behavior of the vehicle.

The actuators 10 include a steering actuator 17, an accelerator openingactuator 18, and a brake control actuator 19.

The steering actuator 17 controls steering direction and the amount ofsteering of the vehicle. The accelerator opening actuator 18 controlsthe accelerator opening of the vehicle. The brake control actuator 19controls braking action of the braking device of the vehicle.

Next, outline of self-location estimation processing performed by theECU 8 will be described. FIG. 2 is now referred to. The referencenumeral 20 indicates a vehicle on which the driving assistance device 1is mounted. The reference numerals 21 and 22 indicate roads existing atdifferent heights h1 and h2, respectively, the reference numerals 21 aand 21 b indicate lane boundary lines (white lines) on the road 21, andthe reference numerals 22 a and 22 b indicate lane boundary lines (whitelines) on the road 22. A case where the vehicle 20 is present on theroad 21 is now assumed.

When the two-dimensional locations of the roads 21 and 22 that exist atdifferent heights are close to each other, it becomes impossible todetermine on which road the vehicle 20 is present only from thetwo-dimensional coordinate information.

Although it is conceivable that, in order to estimate a self-locationincluding height, map matching is performed in a three-dimensional space(for example, a space represented by latitude, longitude, and height),the three-dimensional map matching requires a high computational cost.Therefore, it is preferable to be able to estimate a self-locationincluding height without performing three-dimensional map matching. Asan estimation technology of a self-location, dead reckoning based onwheel speed and angular velocity has been known.

However, in the self-location estimation using the dead reckoning, errorcaused by measurement error accumulates. Therefore, it is necessary toacquire an observed value of height from some information source andcorrect an estimated value calculated using the dead reckoning with theobserved value.

Thus, the driving assistance device 1 acquires height information of atraffic sign 23 in the vicinity of the vehicle 20 that is installed onthe road 21 from the map database and estimates a height at which thevehicle 20 is present, based on the height information of the trafficsign 23.

Specifically, a relative location of the traffic sign 23 with respect tothe vehicle 20 is detected using the external sensors 3. The ECU 8determines a current location of the vehicle 20. For example, the ECU 8estimates the current location of the vehicle 20, using the deadreckoning, based on the wheel speed detected by the wheel speed sensor13 and the pitch angular velocity, the roll angular velocity, and theyaw angular velocity detected by the gyro-sensor 14. For example, theECU 8 may measure the current location of the vehicle 20, using thepositioning device 5.

The ECU 8 acquires height information of the traffic sign 23 from themap database 6 in which two-dimensional coordinate information (forexample, longitude and latitude) and height information of traffic signs23 and 24 existing in the vicinities of the roads are recorded, based onthe two-dimensional coordinates of the current location of the vehicle20 and the relative location of the traffic sign 23.

The ECU 8 estimates a height at which the vehicle 20 is present, basedon the height information acquired from the map database 6. For example,the ECU 8 estimates a height indicated by the height informationacquired from the map database 6 as the height at which the vehicle 20is present.

Correcting an estimated value of the height calculated using the deadreckoning with the height estimated in this manner enables error causedby measurement error to be prevented from accumulating.

In addition, since the height can be estimated without performingthree-dimensional map matching, it is possible to keep the computationalcost low.

Further, since the height is estimated based on the coordinateinformation of the traffic sign 23 recorded in the map database 6, it ispossible to correctly estimate the height at which the vehicle 20 ispresent even when separate roads of the same road type respectivelyexist at different heights and the two-dimensional locations of theroads are close to each other.

Note that, as illustrated in FIG. 2, the traffic sign 24 is installed onthe road 22, which exists at a height different from the height of theroad 21 on which the vehicle 20 is present, as well. However, since thetraffic sign 24 is shielded from the vehicle 20 on the road 21 by theroad structure, the external sensors 3 cannot detect the traffic sign24. Therefore, erroneously estimating the height at which the vehicle 20is present based on the height information of the traffic sign 24, whichis installed on the road 22 that is different from the road 21, neveroccurs. Thus, the height information of a traffic sign does notnecessarily have to be a numerical value representing a height, and itmay be configured to acquire information indicating on which one ofroads that are close to each other the traffic sign is installed. Forexample, when the traffic sign 23 is detected, it is possible to acquireinformation indicating that the installation location of the trafficsign 23 is on the road 21 and determine that the vehicle 20 is travelingon one existing at a higher height of the roads that are close to eachother. On the other hand, when the traffic sign 24 is detected, it ispossible to acquire information indicating that the installationlocation of the traffic sign 24 is on the road 22 and determine that thevehicle 20 is traveling on the other existing at a lower height of theroads that are close to each other.

Next, a functional configuration of the ECU 8 will be described withreference to FIG. 3. The ECU 8 includes a self-location estimation unit30, a target trajectory setting unit 31, and a travel control unit 32.Functions of the self-location estimation unit 30, the target trajectorysetting unit 31, and the travel control unit 32 may be achieved by, forexample, the processor 15 of the ECU 8 executing computer programsstored in the storage device 16.

The self-location estimation unit 30 estimates a self-location of thevehicle, based on various information input from the external sensors 3,the internal sensors 4, and the positioning device 5 and informationacquired with reference to the map database 6.

The self-location estimation unit 30 includes a dead reckoning unit 40,a map matching unit 41, a traffic sign detection unit 42, a coordinatecalculation unit 43, and a height information acquisition unit 44.

The dead reckoning unit 40 calculates a predicted location of thevehicle at a present time point, using the dead reckoning based on thewheel speed, the pitch angular velocity, the roll angular velocity, andthe yaw angular velocity detected by the internal sensors 4. Thepredicted location of the vehicle includes two-dimensional coordinates,a height, and an azimuth of the forward direction of the vehicle.

The dead reckoning unit 40 outputs the calculated predicted location tothe map matching unit 41.

In this processing, the dead reckoning unit 40 calculatestwo-dimensional coordinates in a two-dimensional coordinate system usedin the map database 6. Hereinafter, the two-dimensional coordinatesystem used in the map database 6 is referred to as “map coordinatesystem”.

Although, in the following description, an example in which thetwo-dimensional coordinate system used in the map database 6 is ageographical coordinate system in which the coordinates are representedby latitude and longitude will be described, the two-dimensionalcoordinate system is not limited to the geographical coordinate systemand another coordinate system, such as a plane rectangular coordinatesystem and a polar coordinate system, may be used.

The map matching unit 41 calculates, based on the relative locations ofground objects in the surroundings of the vehicle and relative locationsof white lines, which are detected by the external sensors 3, and thepredicted location of the vehicle, which is calculated by the deadreckoning unit 40, two-dimensional coordinates in the map coordinatesystem of the ground objects and the white lines.

The map matching unit 41 matches the two-dimensional coordinates of theground objects and the white lines with the map database 6, usingtwo-dimensional map matching and calculates a mapping correction valueof the vehicle location with respect to each of latitude, longitude, andazimuth.

The map matching unit 41 corrects the predicted location of the vehicle,which is calculated by the dead reckoning unit 40, with the calculatedmapping correction values and thereby acquires an estimated value of thecurrent location of the vehicle.

The map matching unit 41 outputs the estimated value of the currentlocation of the vehicle to the coordinate calculation unit 43 and thetarget trajectory setting unit 31.

The traffic sign detection unit 42 detects a relative location of atraffic sign, which is detected by the external sensors 3, in thevicinity of the vehicle with respect to the vehicle. The X-coordinateand the Y-coordinate of the relative location of a traffic sign aredenoted as “TS_X [m]” and “TS_Y [m]”, respectively.

The traffic sign detection unit 42 outputs the relative location of thetraffic sign to the coordinate calculation unit 43.

The coordinate calculation unit 43 calculates estimated values of thetwo-dimensional coordinates of the traffic sign in the map coordinatesystem.

As illustrated in FIG. 4, latitude and longitude of the traffic sign aredenoted as “TS_B [rad]” and “TS_L [rad]”, respectively.

The latitude and the longitude of the estimated value of the currentlocation of the vehicle and the azimuth of the forward direction of thevehicle, which are acquired by the map matching unit 41, are denoted as“V_B [rad]”, “V_L [rad]”, and “θ [rad]”, respectively.

The coordinate calculation unit 43 calculates estimated values of thetwo-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic signby approximation in accordance with the formulae (1) and (2) below.

TS_B=V_B+(TS_X sin θ+TS_Y cos θ)/M  (1)

TS_L=V_L+(TS_X cos θ−TS_Y sin θ)/(N cos V_B)  (2)

In the above formulae, M denotes radius of curvature of the meridian [m]and N denotes radius of curvature of the prime vertical [m] at alatitude V_B.

The coordinate calculation unit 43 outputs the estimated values of thetwo-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic signto the height information acquisition unit 44.

The height information acquisition unit 44 matches the two-dimensionalcoordinates (TS_B [rad], TS_L [rad]) of the traffic sign calculated bythe coordinate calculation unit 43 with the two-dimensional coordinateinformation of traffic signs recorded in the map database 6.

When a traffic sign that has two-dimensional coordinate information thatmatches the two-dimensional coordinates (TS_B [rad], TS_L [rad]), whichare calculated by the coordinate calculation unit 43, exists in the mapdatabase 6, the height information acquisition unit 44 acquires thecoordinate information (latitude TS_M_B [rad], longitude TS_M_L [rad],and height TS_M_H [m]) of the matching traffic sign from the mapdatabase 6.

In the above processing, cases where the two-dimensional coordinates(TS_B [rad], TS_L [rad]) and the two-dimensional coordinates (TS_M_B[rad], TS_M_L [rad]) match each other include not only a case where thetwo two-dimensional coordinates completely coincide with each other butalso a case where a difference between the two two-dimensionalcoordinates is less than a predetermined value.

The height information (TS_M_H [m]) of a traffic sign may be heightinformation of the ground (that is, the base) at the installation pointof the traffic sign or height information of the sign plate of thetraffic sign.

Note that a traffic sign the height information of which is to beacquired may be, for example, an information sign, a danger warningsign, a regulatory sign, or a direction sign.

The height information acquisition unit 44 estimates that the height atwhich the vehicle is present is a height that the height information ofthe traffic sign acquired from the map database 6 indicates. The heightinformation acquisition unit 44 may update the estimated value of theheight at which the vehicle is present, using a Kalman filter, based onheight information of the traffic sign that is acquired multiple timesat different time points.

The height information acquisition unit 44 outputs the estimated heightat which the vehicle is present to the dead reckoning unit 40 and thetarget trajectory setting unit 31.

The dead reckoning unit 40 corrects the predicted value of the height atwhich the vehicle is present that is calculated using the deadreckoning, according to the height estimated by the height informationacquisition unit 44. For example, the dead reckoning unit 40 corrects(overwrites) the predicted value of the height at which the vehicle ispresent, which is calculated using the dead reckoning, with the heightestimated by the height information acquisition unit 44 and calculates asubsequent predicted location of the vehicle, based on the correctedheight.

The dead reckoning unit 40 may correct the predicted value of the heightat which the vehicle is present, which is calculated using the deadreckoning, according to the height estimated by the height informationacquisition unit 44 every time the vehicle travels a predetermineddistance. This configuration enables error of the dead reckoning thataccumulates according to travel distance to be efficiently corrected.

The target trajectory setting unit 31 sets a target travel trajectory onwhich the vehicle is required to travel, based on the current locationof the vehicle estimated by the map matching unit 41, the road map datain the map database 6, the route information output from the navigationsystem 7, the surrounding environment detected by the external sensors3, and the travel state of the vehicle detected by the internal sensors4.

On this occasion, the target trajectory setting unit 31 determines aroad on which the vehicle is present based on the two-dimensionalcoordinates of the current location of the vehicle estimated by the mapmatching unit 41 and the height at which the vehicle is presentestimated by the height information acquisition unit 44. For example,when a plurality of roads the heights of which are different from eachother exist at the two-dimensional coordinates of the current locationof the vehicle, the target trajectory setting unit 31 determines onwhich one of the plurality of roads the vehicle is present, based on theheight at which the vehicle is present that is estimated by the heightinformation acquisition unit 44.

The target trajectory setting unit 31 sets a target travel trajectory inwhich the vehicle travels on the road on which the vehicle is present inaccordance with the route generated by the navigation system 7.

The target trajectory setting unit 31 outputs the set target traveltrajectory to the travel control unit 32.

The travel control unit 32 performs the automatic-driving control andthe driving assistance control of the vehicle by driving the actuators10 in such a way that the vehicle travels on the travel trajectorygenerated by the target trajectory setting unit 31 and thereby operatinga steering mechanism, an acceleration mechanism, and a brake mechanismof the vehicle.

(Operation)

Next, an example of a driving assistance method of the embodiment willbe described with reference to FIG. 5.

In step S1, the self-location estimation unit 30 in FIG. 3 performs theself-location estimation processing of estimating a current location ofthe vehicle.

FIG. 6 is a flowchart of an example of the self-location estimationprocessing S1.

In step S10, the dead reckoning unit 40 calculates a predicted location(latitude, longitude, height, and azimuth) of the vehicle at a presenttime point, using the dead reckoning based on the wheel speed, the pitchangular velocity, the roll angular velocity, and the yaw angularvelocity detected by the internal sensors 4.

In step S11, the map matching unit 41 calculates, based on the relativelocations of the ground objects in the surroundings of the vehicle andthe relative locations of the white lines, which are detected by theexternal sensors 3, the predicted location of the vehicle, which wascalculated by the dead reckoning unit 40, and the map database 6, anestimated value of the current location of the vehicle, using thetwo-dimensional map matching.

In step S12, the traffic sign detection unit 42 detects a relativelocation (TS_X [m], TS_Y [m]) of the traffic sign, which is detected bythe external sensors 3, in the surroundings of the vehicle with respectto the vehicle.

In step S13, the coordinate calculation unit 43 calculates estimatedvalues (TS_B [rad], TS_L [rad]) of the two-dimensional coordinates ofthe traffic sign in the map coordinate system.

In step S14, the height information acquisition unit 44 matches thetwo-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic signcalculated in step S13 with the two-dimensional coordinate informationof traffic signs recorded in the map database 6. The height informationacquisition unit 44 determines whether or not a traffic sign that hastwo-dimensional coordinate information matching the two-dimensionalcoordinates (TS_B [rad], TS_L [rad]) exists in the map database 6.

When no traffic sign the two-dimensional coordinates of which match thetwo-dimensional coordinates (TS_B [rad], TS_L [rad]) exists in the mapdatabase 6 (step S14: N), the self-location estimation processing S1 isterminated without correcting the height calculated using the deadreckoning.

When a traffic sign the two-dimensional coordinates of which match thetwo-dimensional coordinates (TS_B [rad TS_L [rad]) exists in the mapdatabase 6 (step S14: Y), the process proceeds to step S15.

In step S15, the height information acquisition unit 44 acquires thecoordinate information (latitude TS_M_B [rad], longitude TS_M_L [rad],and height TS_M_H [m]) of the traffic sign the two-dimensionalcoordinates of which match the two-dimensional coordinates (TS_B [rad],TS_L [rad]) from the map database 6. The height information acquisitionunit 44 estimates that the height at which the vehicle is present is theheight (TS_M_H [m]) of the traffic sign.

In step S16, the dead reckoning unit 40 corrects the predicted value ofthe height at which the vehicle is present, which was calculated usingthe dead reckoning, to the height estimated by the height informationacquisition unit 44. Subsequently, the self-location estimationprocessing S1 is terminated.

FIG. 5 is now referred to. In step S2, the target trajectory settingunit 31 determines a road on which the vehicle is present based on thetwo-dimensional coordinates of the current location of the vehicle,which was estimated by the map matching unit 41, and the height at whichthe vehicle is present, which was estimated by the height informationacquisition unit 44.

When a plurality of roads the heights of which are different from eachother exist at the two-dimensional coordinates of the current locationof the vehicle, the target trajectory setting unit 31 determines onwhich one of the plurality of roads the vehicle is present, based on theheight at which the vehicle is present, which was estimated by theheight information acquisition unit 44. Note that the height informationof the vehicle is only required to be information that enables on whichone of a plurality of roads the heights of which are different from eachother the vehicle is present at the two-dimensional coordinates of thecurrent location of the vehicle to be determined. For example, theheight information of the vehicle may be information that indicates onwhich one of a plurality of different roads a traffic sign, amongtraffic signs respectively installed on the plurality of roads, that thetraffic sign detected by the vehicle matches is installed.

In step S3, the target trajectory setting unit 31 sets a target traveltrajectory in which the vehicle travels on the road on which the vehicleis currently present, based on the current location of the vehicle,which was estimated by the map matching unit 41, the road map data inthe map database 6, the route information output from the navigationsystem 7, the surrounding environment detected by the external sensors3, and the travel state of the vehicle detected by the internal sensors4.

On this occasion, the target trajectory setting unit 31 sets a targettravel trajectory in which the vehicle travels on the road on which thevehicle is present, which was determined in step S2, in accordance withthe route generated by the navigation system 7.

In step S4, the travel control unit 32 performs travel control, such asthe automatic-driving control and the driving assistance control, of thevehicle by driving the actuators 10 in such a way that the vehicletravels on the travel trajectory that was generated by the targettrajectory setting unit 3.

Advantageous Effects of Embodiment

(1) The traffic sign detection unit 42 detects a traffic sign in thevicinity of the vehicle. The dead reckoning unit 40 and the map matchingunit 41 determine a current location of the vehicle. The coordinatecalculation unit 43 and the height information acquisition unit 44acquire the height information of the detected traffic sign from the mapdatabase 6, based on the relative location of the detected traffic signwith respect to the vehicle and the current location and estimate aheight at which the vehicle is present according to the heightinformation.

Since this processing enables the height at which the vehicle is presentto be estimated, it becomes possible to determine on which one of roadsexisting at different heights the vehicle is present.

In particular, since the height is estimated based on the coordinateinformation of the traffic sign 23 recorded in the map database 6, it ispossible to correctly estimate the height at which the vehicle 20 ispresent even when roads of the same road type respectively exist atdifferent heights and the two-dimensional locations of the roads areclose to each other.

(2) The dead reckoning unit 40 and the map matching unit 41 determinetwo-dimensional coordinates of the current location in the mapcoordinate system. The coordinate calculation unit 43 calculatestwo-dimensional coordinates of the detected traffic sign in the mapcoordinate system, based on the two-dimensional coordinates of therelative location of the detected traffic sign and the current location.The height information acquisition unit 44 acquires the heightinformation of a traffic sign that has two-dimensional coordinateinformation corresponding to the two-dimensional coordinates of thedetected traffic sign from the map database 6 as the height informationof the detected traffic sign.

This processing enables the height information of the traffic signdetected in the vicinity of the vehicle to be appropriately acquiredfrom the map database 6, in which two-dimensional coordinate informationand height information of traffic signs existing in the vicinities ofroads are recorded.

(3) The map matching unit 41 calculates two-dimensional coordinates ofthe current location in the map coordinate system, using two-dimensionalmap matching.

That is, the map matching unit 41 calculates two-dimensional coordinatesof the current location, using two-dimensional map matching andestimates a height at which the vehicle is present, based on thecoordinate information of the traffic sign 23 recorded in the mapdatabase 6. Since, because of this configuration, a self-locationincluding height can be estimated without performing three-dimensionalmap matching, it is possible to keep the computational cost low.

(4) The dead reckoning unit 40 corrects the estimated value of theheight at which the vehicle is present, which is calculated using deadreckoning, according to the height information acquired from the mapdatabase 6.

This configuration enables error in the height caused by measurementerror to be prevented from accumulating.

(5) The dead reckoning unit 40 corrects the estimated value according tothe height information acquired from the map database every time thevehicle travels a predetermined distance.

This configuration enables error of the dead reckoning, whichaccumulates as travel distance increases, to be efficiently corrected.

(6) A traffic sign that the traffic sign detection unit 42 detects maybe an information sign. Such information signs are often installed atsites where roads cross each other vertically, such as a junction.Therefore, it is possible to appropriately determine on which one ofroads the vehicle is traveling at a site where the roads cross eachother vertically.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

REFERENCE SIGNS LIST

-   -   1 Driving assistance device    -   2 Self-location estimation device    -   3 External sensor    -   4 Internal sensor    -   5 Positioning device    -   6 Map database    -   7 Navigation system    -   10 Actuator    -   11 Camera    -   12 Ranging device    -   13 Wheel speed sensor    -   14 Gyro-sensor    -   15 Processor    -   16 Storage device    -   17 Steering actuator    -   18 Accelerator opening actuator    -   19 Brake control actuator    -   20 Vehicle    -   21, 22 Road    -   21 a, 21 b, 22 a, 22 b Lane boundary line (white line)    -   23, 24 Traffic sign    -   30 Self-location estimation unit    -   31 Target trajectory setting unit    -   32 Travel control unit    -   40 Dead reckoning unit    -   41 Map matching unit    -   42 Traffic sign detection unit    -   43 Coordinate calculation unit    -   44 Height information acquisition unit

1. A self-location estimation method comprising: detecting a trafficsign in a vicinity of a vehicle; determining a current location of thevehicle; acquiring height information of the detected traffic sign frommap data in which two-dimensional coordinate information of a lane of aroad and two-dimensional coordinate information and height informationof a traffic sign existing in a vicinity of a road are recorded, basedon a relative location of the detected traffic sign with respect to thevehicle and the current location; estimating a height at which thevehicle is present according to the height information acquired from themap data; determining, when a plurality of roads the heights of whichare different from each other exist at a two-dimensional coordinate ofthe current location of the vehicle, on which one of the plurality ofroads the vehicle is present, based on the estimated height; setting atarget travel trajectory of the vehicle based on a two-dimensionalcoordinate of the lane and the two-dimensional coordinate of the currentlocation of the vehicle such that the vehicle travels along a route on atwo-dimensional coordinate system generated by a navigation system onthe lane of the road of the plurality of road on which the vehicle ispresent; and driving an actuator to operate a steering mechanism of thevehicle such that the vehicle travels on the target travel trajectory.2. The self-location estimation method according to claim 1 comprising:determining the two-dimensional coordinate of the current location in acoordinate system of the map data; calculating a two-dimensionalcoordinate of the detected traffic sign in the coordinate system, basedon a two-dimensional coordinate of the relative location of the detectedtraffic sign and the current location; and acquiring height informationof a traffic sign having two-dimensional coordinate informationcorresponding to the two-dimensional coordinate of the detected trafficsign from the map data as height information of the detected trafficsign.
 3. The self-location estimation method according to claim 2comprising: calculating the two-dimensional coordinate of the currentlocation in the coordinate system, using two-dimensional map matching.4. The self-location estimation method according to claim 1 comprising:correcting an estimated value of a height at which the vehicle ispresent, the estimated value being calculated using dead reckoning,according to the height information acquired from the map data.
 5. Theself-location estimation method according to claim 4 comprising:correcting the estimated value according to the height informationacquired from the map data every time the vehicle travels apredetermined distance.
 6. The self-location estimation method accordingto claim 1, wherein the traffic sign is an information sign.
 7. Aself-location estimation device comprising: a sensor configured todetect a traffic sign in a vicinity of a vehicle; an actuator to controla steering mechanism of the vehicle and a controller configured to:determine a current location of the vehicle; acquire height informationof the detected traffic sign from map data in which two-dimensionalcoordinate information of a lane of a road and two-dimensionalcoordinate information and height information of a traffic sign existingin a vicinity of a road are recorded, based on a relative location ofthe detected traffic sign with respect to the vehicle and the currentlocation; estimate a height at which the vehicle is present according tothe height information acquired from the map data; determine, when aplurality of roads the heights of which are different from each otherexist at the two-dimensional coordinates of the current location of thevehicle, on which one of the plurality of roads the vehicle is present,based on the estimated height; set a target travel trajectory of thevehicle based on a two-dimensional coordinate of the lane and thetwo-dimensional coordinate of the current location of the vehicle suchthat the vehicle travels along a route on a two-dimensional coordinatesystem generated by a navigation system on the lane of the road of theplurality of road on which the vehicle is present; and drive an actuatorto operate a steering mechanism of the vehicle such that the vehicletravels on the target travel trajectory.